Specify a local IP address or a hostname the
ntpd(8) daemon should listen
on. If it appears multiple times,
ntpd(8) will listen on each
given address. If ‘*’ is given as an address,
ntpd(8) will listen on all
local addresses using the specified routing table.
ntpd(8) does not listen on any
address by default. The optional rtable
keyword will specify which routing table to listen on. By default
ntpd(8) will listen using the
current routing table. For example:

Specify a timedelta sensor device
ntpd(8) should use. The sensor
can be specified multiple times:
ntpd(8) will use each given
sensor that actually exists. Non-existent sensors are ignored. If
‘*’ is given as device name,
ntpd(8) will use all timedelta
sensors it finds. ntpd(8) does
not use any timedelta sensor by default. For example:

sensor *
sensor nmea0

An optional correction in microseconds can be given to compensate for the
sensor's offset. The maximum correction is 127 seconds. For example, if a
DCF77 receiver is lagging 70ms behind actual time:

sensor udcf0 correction 70000

The optional weight keyword permits finer
control over the relative importance of time sources (servers or sensor
devices). Weights are specified in the range 1 to 10; if no weight is
given, the default is 1. A server with a weight of 5, for example, will
have five times more influence on time offset calculation than a server
with a weight of 1.

An optional reference ID string - up to 4 ASCII characters - can be given to
publish the sensor type to clients. RFC 2030 suggests some common
reference identifiers, but new identifiers "can be contrived as
appropriate." If an ID string is not given,
ntpd(8) will use a generic
reference ID. For example:

sensor nmea0 refid GPS

A stratum value other than the default of 1 can be assigned using the
stratum keyword.

Specify the IP address or the hostname of an NTP server to synchronize to.
If it appears multiple times,
ntpd(8) will try to
synchronize to all of the servers specified. If a hostname resolves to
multiple IPv4 and/or IPv6 addresses,
ntpd(8) uses the first
address. If it does not get a reply,
ntpd(8) retries with the next
address and continues to do so until a working address is found. For
example:

server 10.0.0.2 weight 5
server ntp.example.org weight 1

To provide redundancy, it is good practice to configure multiple servers. In
general, best accuracy is obtained by using servers that have a low
network latency.

As with server, specify the IP address
or hostname of an NTP server to synchronize to. If it appears multiple
times, ntpd(8) will try to
synchronize to all of the servers specified. Should the hostname resolve
to multiple IP addresses,
ntpd(8) will try to
synchronize to all of them. For example:

ntpd(8) can be configured to query
the ‘Date’ from trusted HTTPS servers via TLS. This time
information is not used for precision but acts as an authenticated constraint,
thereby reducing the impact of unauthenticated NTP man-in-the-middle attacks.
Received NTP packets with time information falling outside of a range near the
constraint will be discarded and such NTP servers will be marked as invalid.

Specify the URL, IP address or the hostname of an HTTPS server to provide
a constraint. If constraint from is
used more than once, ntpd(8)
will calculate a median constraint from all the servers specified.

As with constraint from, specify the
URL, IP address or the hostname of an HTTPS server to provide a
constraint. Should the hostname resolve to multiple IP addresses,
ntpd(8) will calculate a
median constraint from all of them. For example: